Biomedical subjects

Xiaoyun Chen

Publications and source records attributed to Xiaoyun Chen.

16 recordsLinked to original sources

PubMed2007

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy.

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Adsorption↗

PubMed2006

Differential effects of endoplasmic reticulum stress-induced autophagy on cell survival.

Autophagy is a cellular response to adverse environment and stress, but its significance in cell survival is not always clear. Here we show that autophagy could be induced in the mammalian cells by chemicals, such as A23187, tunicamycin, thapsigargin, and brefeldin A, that cause endoplasmic reticulum stress. Endoplasmic reticulum stress-induced autophagy is important for clearing polyubiquitinated protein aggregates and for reducing cellular vacuolization in HCT116 colon cancer cells and DU145 prostate cancer cells, thus mitigating endoplasmic reticulum stress and protecting against cell death. In contrast, autophagy induced by the same chemicals does not confer protection in a normal human colon cell line and in the non-transformed murine embryonic fibroblasts but rather contributes to cell death. Thus the impact of autophagy on cell survival during endoplasmic reticulum stress is likely contingent on the status of cells, which could be explored for tumor-specific therapy.

Animals↗

PubMed2006

Bid-independent mitochondrial activation in tumor necrosis factor alpha-induced apoptosis and liver injury.

The death receptor apoptosis pathway is intimately connected with the mitochondrial apoptosis pathway. Bid is a BH3-only pro-death Bcl-2 family protein and is the major molecule linking the two pathways. Bid-mediated mitochondrial activation occurs early and is responsible for the prompt progress of tumor necrosis factor alpha (TNF-alpha)-induced apoptosis. However, in both cultured cells and animal models of TNF-alpha-induced injury, later-phase Bid-independent mitochondrial activation could be demonstrated. Consequently, bid-deficient mice are still susceptible to endotoxin-induced liver injury and mortality. Notably, embryonic hepatocyte apoptosis and lethality caused by TNF-alpha in the absence of p65relA cannot be rescued by the simultaneous deletion of bid. Further studies indicate that multiple mechanisms including reactive oxygen species, JNK, and permeability transition are critically involved in Bid-independent mitochondrial activation. Inhibition of these events suppresses TNF-alpha-induced mitochondrial activation and apoptosis in bid-deficient cells. These findings thus indicate that there are at least two sets of mechanisms of mitochondrial activation upon TNF-alpha stimulation. While the Bid-mediated mechanism is rapid and potent, the Bid-independent mechanism progresses gradually and involves multiple players. The critical involvement of Bid-independent mitochondrial activation in TNF-alpha-induced apoptosis demands the intervention of TNF-alpha-mediated tissue injury via multiple avenues.

Animals↗

PubMed2006

Vibrational spectroscopic studies on fibrinogen adsorption at polystyrene/protein solution interfaces: hydrophobic side chain and secondary structure changes.

Structural changes of fibrinogen after adsorption to polystyrene (PS) were examined at the PS/protein solution interface in situ using sum frequency generation (SFG) vibrational spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Different behaviors of hydrophobic side chains and secondary structures of adsorbed fibrinogen molecules have been observed. Our results indicate that upon adsorption, the hydrophobic PS surface induces fast structural changes of fibrinogen molecules by aligning some hydrophobic side chains in fibrinogen so that they face to the surface. Such structural changes of fibrinogen hydrophobic side chains are local changes and do not immediately induce significant changes of the protein secondary structures. Our research also shows that the interactions between adsorbed fibrinogen and the PS surface can induce significant changes of protein secondary structures or global conformations which occur on a much longer time scale.

Adsorption↗

PubMed2006

Observing a molecular knife at work.

Sum frequency generation (SFG) vibrational spectroscopy has been employed to study the molecular interactions between a single substrate supported lipid bilayer and an amphiphilic antibiotic compound 1, with a design based on the common structural motif of natural antimicrobial peptides. The interfacial sensitivity of SFG allows real-time in situ monitoring of ordering changes in both leaflets of the bilayer and orientation of 1 simultaneously. A critical concentration of about 0.8 microg/mL of 1 is found, above which the inner leaflet of the bilayer is significantly perturbed. This concentration corresponds well to the minimum inhibition concentration of 1 that is obtained from bacterial experiments. Orientation of 1 in the bilayer is shown to be perpendicular to the bilayer surface, in agreement with simulation results. SFG can be developed into a very informative technique for studying the cell membrane and the interactions of membrane-active molecules.

Amides↗

PubMed2006

SFG studies on interactions between antimicrobial peptides and supported lipid bilayers.

The mode of action of antimicrobial peptides (AMPs) in disrupting cell membrane bilayers is of fundamental importance in understanding the efficiency of different AMPs, which is crucial to design antibiotics with improved properties. Recent developments in the field of sum frequency generation (SFG) vibrational spectroscopy have made it a powerful and unique biophysical technique in investigating the interactions between AMPs and a single substrate supported planar lipid bilayer. We will review some of the recent progress in applying SFG to study membrane lipid bilayers and discuss how SFG can provide novel information such as real-time bilayer structure change and AMP orientation during AMP-lipid bilayer interactions in a very biologically relevant manner. Several examples of applying SFG to monitor such interactions between AMPs and a dipalmitoyl phosphatidylglycerol (DPPG) bilayer are presented. Different modes of actions are observed for melittin, tachyplesin I, d-magainin 2, MSI-843, and a synthetic antibacterial oligomer, demonstrating that SFG is very effective in the study of AMPs and AMP-lipid bilayer interactions.

Anti-Bacterial Agents↗

PubMed2006

Inference in multiply sectioned Bayesian networks: methods and performance comparison.

This paper extends lazy propagation for inference in single-agent Bayesian networks (BNs) to multiagent lazy inference in multiply sectioned BNs (MSBNs). Two methods are proposed using distinct runtime structures. It was proved that the new methods are exact and efficient when the domain structure is sparse. Both improve space and time complexity more than the existing method, which allows multiagent probabilistic reasoning to be performed in much larger domains given the computational resource. The relative performances of the three methods are compared analytically and experimentally.

Algorithms↗

PubMed2005

Probing alpha-helical and beta-sheet structures of peptides at solid/liquid interfaces with SFG.

We demonstrated that sum frequency generation (SFG) vibrational spectroscopy can distinguish different secondary structures of proteins or peptides adsorbed at solid/liquid interfaces. The SFG spectrum for tachyplesin I at the polystyrene (PS)/solution interface has a fingerprint peak corresponding to the B1/B3 mode of the antiparallel beta-sheet. This peak disappeared upon the addition of dithiothreitol, which can disrupt the beta-sheet structure. The SFG spectrum indicative of the MSI594 alpha-helical structure was observed at the PS/MSI594 solution interface. This research validates SFG as a powerful technique for revealing detailed secondary structures of interfacial proteins and peptides.

Peptides↗

PubMed2005

Detection of chiral sum frequency generation vibrational spectra of proteins and peptides at interfaces in situ.

In this work, we demonstrate the feasibility to collect off-electronic resonance chiral sum frequency generation (SFG) vibrational spectra from interfacial proteins and peptides at the solid/liquid interface in situ. It is difficult to directly detect a chiral SFG vibrational spectrum from interfacial fibrinogen molecules. By adopting an interference enhancement method, such a chiral SFG vibrational spectrum can be deduced from interference spectra between the normal achiral spectrum and the chiral spectrum. We found that the chiral SFG vibrational spectrum of interfacial fibrinogen was mainly contributed by the beta-sheet structure. For a beta-sheet peptide tachyplesin I, which may be quite ordered at the solid/liquid interface, chiral SFG vibrational spectra can be collected directly. We believe that these chiral signals are mainly contributed by electric dipole contributions, which can dominate the chiroptical responses of uniaxial systems. For the first time, to our knowledge, this work indicates that the off-electronic resonance SFG technique is sensitive enough to collect chiral SFG vibrational spectra of interfacial proteins and peptides, providing more structural information to elucidate interfacial protein and peptide structures.

Animals↗

PubMed2005

Deletion of Bid impedes cell proliferation and hepatic carcinogenesis.

Mechanisms that control the proliferation capability of the initiated cells during hepatocarcinogenesis are still largely unclear. We investigated the role of a pro-death Bcl-2 family protein, Bid, in liver tumor development using a neonatal diethylnitrosamine model. Diethylnitrosamine was administrated to 15-day-old wild-type and bid-null mice. The development of microfoci at the early stage and of gross tumors at the later stage was compared between the two groups of mice. Both microfoci and gross tumor development were significantly retarded in the bid-null mice, despite reduced cell death as measured by TUNEL staining. Further studies indicated that there were significantly less proliferating cells in diethylnitrosamine-treated bid-null livers. The regulation of cell proliferation by Bid was confirmed in two other systems not involving carcinogenesis. Hepatocyte proliferation following partial hepatectomy and T lymphocyte proliferation following anti-CD3 stimulation were both retarded in bid-null mice. Thus, these studies revealed a previously undisclosed function of Bid in regulating cell proliferation, which can be important to tumor development. Furthermore, the role of Bid in promoting hepatocarcinogenesis is in contrast to its reported role in suppressing myeloid leukemia and thus suggests an organ- and/or etiology-specific role of the Bcl-2 family proteins in regulating oncogenesis.

Animals↗

PubMed2004

[Effects of different vegetation restoration of degraded red soil on earthworm population dynamics].

This study was conducted at the long-term experimental plots in Ecological Experimental Station of Red Soil in Yujiang County (28 degrees 15'30''N, 116 degrees 55'30''E ), Jiangxi Province, subtropical China. Earthworm population was investigated seasonally from May 1999 to February 2000, under different vegetations including four artificial woodlands [deciduous broadleaf woodland (Quercus chenii, Qc), evergreen broadleaf woodland (Schima superba, Ss), coniferous woodland (Pinus massonina, Pm) and mixed woodland (Schima superba-Pinus massonina, Sm)], two grasslands [gently-disturbed grassland (G1), undisturbed grassland (G2)] and control wasteland (CK). The results indicated that the population structure was very simple. Only Drawinda gisti characterized by pioneer was found. The seasonal averages of density and biomass were in the order of G2 > G1 > Qc > Ss > Pm > Sm > CK, and those of G2, G1 and Qc were significantly higher than those of the latters (P < 0.05). Seasonal fluctuations were obvious with dry-hot summer depressing the earthworm population sharply, leading to the aestivation of earthworm. Based on the variation coefficients of density and biomass, Qc had the highest ecosystem stability, followed by Sm and Ss, and G1, G2, and Pm had the lowest stability. The overall differentiation of earthworm population could be drawn through canonical discriminant analysis. There were significant correlations between earthworms and some soil properties (P < 0.01). Overall, the differentiation of earthworm population was driven by the quantity and quality of soil organic matter returned by the vegetations. Additionally, based on earthworm population, the importance of selecting appropriate vegetation types during the restoration of degraded red soil was emphasized.

Animals↗

PubMed2003

Detection of amide I signals of interfacial proteins in situ using SFG.

In this Communication, we demonstrate the novel observation that it is feasible to collect amide signals from polymer/protein solution interfaces in situ using sum frequency generation (SFG) vibrational spectroscopy. Such SFG amide signals allow for acquisition of more detailed molecular level information of entire interfacial protein structures. Proteins investigated include bovine serum albumin, mussel protein mefp-2, factor XIIa, and ubiquitin. Our studies indicate that different proteins generate different SFG amide signals at the polystyrene/protein solution interface, showing that they have different interfacial coverage, secondary structure, or orientation.

Absorption↗

PubMed2003

[Effect of bacterivorous nematodes on bacteria population under gnotobiotic culture].

A gnotobiotic microcosm experiment was conducted to study the influence of bacterivorous nematodes (Protorhabditis sp.) on bacteria (Pseudomonas fluorescens) population under different conditions including substrate concentration, oscillation pattern, and numbers of nematodes inoculated. When the bacteria were incubated under intermittent oscillation by hand (6 times at 0.5 h intervals, 22 degrees C), their growth was stimulated in the presence of nematoedes, and the bacteria grew faster with the increase of nematode numbers and substrate (liquid potato-sucrose medium) concentration. However, when the incubation was under continuous oscillation (100 rpm, 22 degrees C), bacteria population was deflated with the addition of nematodes, and the inhibition was greater when a higher concentration of substrate was used. It was found that the stimulation or inhibition of bacteria population by nematodes occurred in the logarithmic stage of bacteria growth. The optimal and over-grazing of nematodes on regulating bacteria population was discussed.

Animals↗

PubMed2002

Sequence and analysis of rice chromosome 4.

Rice is the principal food for over half of the population of the world. With its genome size of 430 megabase pairs (Mb), the cultivated rice species Oryza sativa is a model plant for genome research. Here we report the sequence analysis of chromosome 4 of O. sativa, one of the first two rice chromosomes to be sequenced completely. The finished sequence spans 34.6 Mb and represents 97.3% of the chromosome. In addition, we report the longest known sequence for a plant centromere, a completely sequenced contig of 1.16 Mb corresponding to the centromeric region of chromosome 4. We predict 4,658 protein coding genes and 70 transfer RNA genes. A total of 1,681 predicted genes match available unique rice expressed sequence tags. Transposable elements have a pronounced bias towards the euchromatic regions, indicating a close correlation of their distributions to genes along the chromosome. Comparative genome analysis between cultivated rice subspecies shows that there is an overall syntenic relationship between the chromosomes and divergence at the level of single-nucleotide polymorphisms and insertions and deletions. By contrast, there is little conservation in gene order between rice and Arabidopsis.

Arabidopsis↗

PubMed2002

[Effect of earthworm inoculation on soil carbon and nitrogen dynamics and on crop yield with application of corn residues].

This study was carried out in the Experimental Station of Nanjing Agricultural University, which is in a subtropical monsoon region characterized by a warm-wet spring and a hot-dry summer. The annual average temperature, precipitation and evaporation are 15.6 degrees C, 1010 mm and 1560 mm, respectively. In 1999, the experimental plots (2.8 m x 1.0 m x 0.6 m) were established by concrete frame. Soil in the plots was orthic aquisols collected from Rugao County, Jiangsu Province. Crop rotation was upland rice and winter wheat. At the beginning of the first crop (rice) season, earthworms (Pheretima sp.) were inoculated at a density of 10.m-2 and 20.m-2, respectively, in the plots with an application of corn residues at the rate of 1500 g.m-2(750 g.m-2 in the following seasons). The responses of soil carbon and nitrogen and crop yield to earthworm activity were investigated from 1999 to 2001. The results showed that earthworms had no significant influences on total soil carbon and nitrogen content, which implied that there was no depletion of soil carbon and nitrogen pools in the presence of earthworms. The maintenance of soil carbon might be explained by low assimilation efficiency of organic matter by earthworms, and by the compensation of carbon returning from plant production enhancement. Soil mineral nitrogen, soil microbial biomass carbon and microbial biomass nitrogen were increased, and nitrogen mineralization was strengthened by earthworm activities, which was more obvious at jointing/booting and heading stages. In comparison with no-worm treatments, the yield of rice wheat increased by 9.3% and 5.1%, respectively, in the treatments inoculated with earthworms. It was concluded that earthworm was very important in promoting nitrogen recycling of crop residues and plant productivity, and in keeping the balance of soil carbon pool as well.

Agriculture↗

PubMed2002

[Evaluating the impact of human papilloma virus infection on prognosis of juvenile laryngeal papilloma].

OBJECTIVE: To evaluate the relationship between human papilloma virus (HPV) and pathological characteristics of juvenile laryngeal papillomas (JLP). METHOD: Using polymerase chain reaction protocol, we analyzed paraffin embedded tissue in 25 cases of juvenile laryngeal papilloma and determined the HPV type. RESULT: A total HPV infection positive rate was 96%, and HPV11 positive rate was 56%, HPV6 positive rate was 40%. None of all was positive for HPV16, 18, 33, 71% of patients need tracheotomy in HPV11 infection group, and 30% of patients need tracheotomy in HPV6 infecting group. The post-operation relapse rate in HPV11-positive group was 86% ,and in HPV6-positive group was 40%. CONCLUSION: Juvenile laryngeal papilloma is associated with HPV11, HPV6 infection and we considered that HPV11 infection may be the important guideline of the evaluation of disease prognosis.

Child↗